1. Field of the Invention
This invention relates to a process for isolating and recovering butene-1 of high purity at a high yield from a butane-butene fraction containing isobutylene and butene-1.
2. Prior Art
In order to isolate butene-1 from a butane-butene fraction containing isobutylene and butene-1, C.sub.4 -hydrocarbons other than butene-1 must be removed from the fraction by rectification. However, isobutylene cannot be removed by a simple distillation operation since the volatility of isobutylene resembles closely that of butene-1, in other words the difference in relative volatility between them is too small. For this reason, butene-1 of high purity could not be isolated through simple distillation or rectification process.
In order to isolate butene-1 of high purity from a butane-butene fraction containing isobutylene and butene-1, it is essential to remove isobutylene from the fraction substantially completely.
One of the known processes for removing isobutylene from the butane-butene fraction is the extraction process by the use of sulfuric acid. However, this known process requires a vast investment because an expensive material must be used for the facilities or apparatuses for effecting the process so that they withstand the corrosive action of sulfuric acid. Another known method of separating isobutylene is the absorption method by the use of zeolite. However, butene-1 cannot be satisfactorily separated from butene-2 by this known method.
In general, isobutylene is dimerized or polymerized by the use of an acidic catalyst. It has been proposed to remove the thus formed dimer and/or polymers from the butane-butene fraction by distillation. However, during this dimerization or polymerization reaction, butene-1 tends to be isomerized to be converted to butene-2. There is also a tendency that butene-1 is copolymerized with isobutylene to form co-oligomers.
It is, therefore, necessary to polymerize isobutylene while suppressing the undesired side reactions as little as possible in order to isolate and recover butene-1 at a high yield.
Silica-alumina, activated clay and strong acidic cation exchange resins have been known and used as catalysts for oligomerizing isobutylene. However, undesired side reactions of butene-1 cannot be suppressed completely by the use of these known catalysts.